Package with a cmos die positioned underneath a mems die

ABSTRACT

A package is provided. The package has a substrate and a cover. A MEMS die is provided having a diaphragm. A CMOS die is provided wherein at least a portion of the CMOS die is positioned between the diaphragm and the substrate.

TECHNICAL FIELD

This invention relates to packages for MEMS transducers and particularlyto MEMS packages with a reduced footprint.

BACKGROUND

It has been known in the art to build packages for containingmicro-electromechanical systems (“MEMS”) microphones. A typical packageincludes the MEMS transducer die, along with a separate complimentarymetal-oxide-semiconductor (“CMOS”) die for amplification of the signalarising from the MEMS transducer die. These die are mounted onto asubstrate in a side-by-side formation within a package and wire bondedto each other and the substrate. For an example of this type ofconfiguration, one can reference U.S. Pat. Nos. 6,781,231 and 7,242,089,the disclosures of which are incorporated herein by reference (includingmaterials used to construct such types of packages, MEMS dies, and CMOSdies; dimension ranges for all parts/components; mechanical and/orelectrical coupling methods; and any related manufacturing details).FIG. 1 also provides an example of this configuration. A package 101comprises a substrate 102 and a cover 103. The package 101 has a MEMStransducer die 104 and a CMOS die 106 attached to the substrate 102.Because of the location of an acoustic port 108 above the transducer104, a diaphragm 105 of the transducer 104 divides the package 101 intoa back volume 107 and a front volume 109 (adjacent to the acoustic port108). It is desirable to reduce the footprint of packages, such as thosedescribed above, to better fit into a variety of consumer electronicdevices, such as cell phones, music players, computing devices, etc.

To this end, attempts have been made to stack the dies of a givenpackage to reduce the footprint of the package. See, for example, thepackage 201 of FIG. 2. In this configuration, a CMOS die 206 is placedat least partially under a MEMS die 204 to reduce the footprint of thepackage. A major drawback with placement of the CMOS die 206 underneaththe MEMS die 204 is that by doing so, either the height of the packageis increased or if the MEMS die 204 is thinned, the back volume 207 ofthe package is decreased, thereby negatively impacting the microphonesensitivity and signal to noise ratio. It is at least one objective ofthe present invention to address this drawback.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosure, reference should bemade to the following detailed description and accompanying drawingswherein:

FIG. 1 is a cross-sectional view of a prior art package containing aseparate CMOS and MEMS die in a side by side configuration;

FIG. 2 is a cross-sectional view of a prior art package comprisingseparate CMOS and MEMS die in a stacked configuration;

FIG. 3 is a cross-sectional view of a package having a CMOS die locatedunderneath a MEMS die in an embodiment of the present invention;

FIG. 4 is a cross-sectional view of a further embodiment of the presentinvention in which a package has a CMOS die located under a MEMS die,wherein the CMOS die is flip chip mounted, and the MEMS die is wirebonded, and wherein the acoustic port is located in a substrate;

FIG. 5 is a cross-sectional view of a further embodiment of a package ofthe present invention in which a package has a CMOS die located under aMEMS die, and wherein the acoustic port is located in a substrateunderneath the MEMS die;

FIG. 6 is a cross-sectional view of a further embodiment of a package ofthe present invention in which a package has a CMOS die located under aMEMS die, wherein the acoustic port is located in a substrate but offsetfrom the CMOS die;

FIG. 7 is a bottom perspective view of a MEMS die in an embodiment ofthe present invention, whereby the MEMS die contains a partial cutthrough the sidewalls of a back chamber;

FIG. 8 is a perspective view of an embodiment of the present inventionin which a CMOS die is partially nested under a MEMS die containing apartial cut through the sidewalls of the back chamber; and

FIG. 9 is a cross-sectional view of a package in an embodiment of thepresent invention in which a CMOS die is partially nested under a MEMSdie with a partial cut through the sidewalls of the back chamber andwherein the MEMS die has channels associated therewith.

DETAILED DESCRIPTION OF THE INVENTION

While the invention of the present disclosure is susceptible to variousmodifications and alternative forms, certain embodiments are shown byway of example in the drawings and these embodiments will be describedin detail herein. It will be understood, however, that this disclosureis not intended to limit the invention to the particular formsdescribed, but to the contrary, the invention is intended to cover allmodifications, alternatives, and equivalents falling within the spiritand scope of the invention defined by the appended claims. Moreover, itis understood that like numerals will refer to like parts.

As mentioned above, the diaphragm of a MEMS microphone effectivelydivides the package into two acoustic volumes, denoted the front volumeand the back volume. The front volume is the portion of the packagewhich is adjacent to the acoustic port while the back volume is thatportion of the package which is on the side of the diaphragm opposite towhere the acoustic port is located, The size of the back volume is a keyacoustic parameter and contributes to the microphone sensitivity andsignal to noise ratio. Maximization of the back volume can lead tomaximization of the acoustic performance of the microphone.

In an embodiment, a package is provided. The package has a substrate anda cover. A MEMS die is located on the substrate. A CMOS die is locatedunderneath the MEMS die. The CMOS die has a volume. An acoustic port islocated in the package, wherein the package has a back volume locatedbetween the MEMS die and the substrate. An effective back volume existswhich is equal to the back volume minus the volume of the CMOS die.

In an embodiment, the acoustic port is in the cover,

In an embodiment, the acoustic port is in the substrate.

In an embodiment, the package has a channel created within the MEMS diewherein the CMOS die is partially nested underneath the MEMS die.

In another embodiment, a package is provided. The package has asubstrate and a cover. A MEMS die is located on the substrate. A CMOSdie is located underneath the MEMS die. The CMOS die has a volume. Anacoustic port is provided in the package, wherein the package has afront volume located between the MEMS die and the substrate. Aneffective front volume exists which is equal to the front volume minusthe volume of the CMOS die.

In an embodiment, the acoustic port is located in the substrate,

In an embodiment, the acoustic port is positioned adjacent to the CMOSdie.

In another embodiment, a package is provided. The package has asubstrate and a cover. A MEMS die is provided which has sidewalls and adiaphragm connected to the sidewalls. A CMOS die is positioned on thesubstrate, underneath the MEMS die and surrounded by the sidewalls ofthe MEMS die.

In an embodiment, the package has an acoustic port within the cover.

In an embodiment, the package has an acoustic port within the substrate.

In another embodiment, a package is provided. The package has asubstrate and a cover. A MEMS die is provided having sidewalls and adiaphragm connected to the sidewalls. A CMOS die is positioned on thesubstrate, partially underneath the MEMS die and through a channel in asidewall of the MEMS die.

In an embodiment, the package has a sealant enclosing a portion of theCMOS die which is positioned exterior to the MEMS die.

In an embodiment, the package has an acoustic port within the substrate.

In an embodiment, the package has an acoustic port within the cover.

In another embodiment, a package is provided. The package has asubstrate and a cover. A MEMS die is provided having a diaphragm. A CMOSdie is provided wherein at least a portion of the CMOS die is positionedbetween the diaphragm and the substrate.

In an embodiment, the CMOS die is contained within sidewalls of the MEMSdie.

In an embodiment, the CMOS die extends through a channel in the MEMSdie.

In an embodiment, the package has a sealant enclosing a portion of theCMOS die which extends exterior to the MEMS die.

In an embodiment, the package has an acoustic port within the substrate.

In an embodiment, the package has an acoustic port within the cover.

The present invention seeks to counter the teachings against placing theCMOS die underneath the MEMS die and thereby reducing the volumeunderneath the MEMS die. In a first embodiment of the present invention,illustrated in FIG. 3, a package 301 contains a CMOS die 306 underneatha MEMS transducer die 304. An acoustic port 308 is above the MEMS die304; therefore, the package 301 has a front volume 309 and a back volume307 on a side of a diaphragm 305 opposite to the acoustic port 308, Inorder to reduce the footprint of the package 301, it is possible toincrease the dimensions of the MEMS die 304 to accommodate the placementof the CMOS die 306 underneath the MEMS die 304 and within the backchamber or back volume 307 of the MEMS die 304. The increased backchamber volume 307, less the volume of the CMOS die 306, will provide anoverall back volume that will exceed the back volume of the conventionalimplementation that is known in the art, i.e., that of FIG. 1.Increasing the dimensions of the MEMS die 304 may increase the overallcost of manufacture of the MEMS die 304. However, the increased cost iscompensated by the overall reduced size and/or cost of the package.Thus, a package having a reduced footprint is achieved with the same orbetter performance acoustically, while demonstrating a cost comparableto that of a conventional package known in the art.

The following is an embodiment of the present invention in which, forexample, the package 301 is configured to provide an acousticperformance similar to the package 101. Assuming the MEMS die 104 inFIG. 1 has dimensions 1.1 mm×1.1 mm×0.4mm, with a back chamber havingdimensions that are 0.74 mm×0.74 mm×0.4 mm, the back chamber volume(otherwise understood as the volume underneath the diaphragm 305) is0.22 mm̂3. The CMOS die 106 has dimensions of 0.5 mm×0.5 mm×0.2 mm for avolume of 0.05 mm̂3. To achieve the same level of performance in theembodiment in FIG, 3 as that in FIG. 1, the dimensions of the MEMS die304 must increase to 1.2 mm×1.2 mm×0.4 mm, to provide a back chamberhaving dimensions of 0.84 mm×0.84 mm×0.4 mm. This provides a backchamber volume of 0.28mm̂3. When the CMOS die 306 is placed underneathand within the back chamber of the MEMS die 304, the effective backvolume (or volume of back chamber minus the volume of the CMOS die 306)becomes 0.23mm̂3 which is slightly larger than that of the back volume107 of the package 101 of FIG. 1. Thus, a slightly better performancecan be achieved by nesting the CMOS die under the larger-sized MEMS die.The larger MEMS die may be, for example, 20% more expensive tomanufacture; however, the package size (and therefore, cost) can bereduced to compensate for the increased cost of the MEMS.

Referring now to FIG. 4, an embodiment is shown in which a package 401(having substrate 402 and cover 403) contains a MEMS die 404 and a CMOSdie 406 located underneath the MEMS die 404. The entire CMOS die 406 islocated between sidewalls 414 of the MEMS die 404. The CMOS die 406 isshown as flip chip bonded while the MEMS die 404 is wire bonded. Itshould be understood, however, that any type of coupling known to thoseskilled in the art is contemplated, The MEMS die 404 may have dimensionssuch that an overall or effective back volume 407 of the package 401(i.e., volume underneath the diaphragm minus the volume of the CMOS die406) is sufficient to produce an acoustic performance demonstrated byconventional transducer packages. In this embodiment, an acoustic port408 is provided in the substrate 402 and is adjacent to the MEMS die404.

FIG. 5 illustrates a package 501 in another embodiment of the presentinvention. A CMOS die 506 is located underneath a MEMS transducer die504, An acoustic port 508 is located under the CMOS die 506 in substrate502. Because the acoustic port 508 is located underneath the MEMS die504, the back volume 507 is defined as that portion of the package 501that is between the cover 503 and the MEMS die 504. The front volume 509is that portion under the MEMS die 504, less the volume of the CMOS die506. In this case, the back volume 507 is increased by having the CMOSdie 506 in the front volume 509. Accordingly, the package 501 maydemonstrate sensitivity and signal-to-noise characteristics as seen inconventional packages while providing a smaller overall footprint.

FIG. 6 illustrates an embodiment similar to that of FIG. 5; however, inthis embodiment, the acoustic port 608 is adjacent to the CMOS die 606,rather than under it. However, both the CMOS die 606 and the acousticport 608 are under the MEMS die 604. In this embodiment, the frontvolume 609 is defined as the volume between the acoustic port 608 andthe diaphragm 605. It is contemplated that, in this embodiment, the MEMSdie 604 may have dimensions, at least in length and/or width, which aregreater than the MEMS die 304, 404, 504 previously described. It is alsocontemplated that, in an embodiment, the MEMS die 604 is sized topartially cover the acoustic port 608. Moreover, it is furthercontemplated that, in an embodiment, the acoustic port 608 is located inthe substrate 602 but only partially underneath the CMOS die 606.

Referring now to FIG. 7, a MEMS die 704 is illustrated which has beenmodified by etching or cutting a channel 710 partially through thesidewalls 714 of the back chamber 716. The preferred method to achievethis channel 710 is by partially dicing with a dicing saw; however,other methods are available as contemplated by those of skill in theart. The MEMS die 704 of this embodiment may be utilized in packages 801and 901 described below. The channel 710 is rectangular in shape;however, other shapes may be used as necessary for a given application.

FIG. 8 shows an isolated view of a MEMS die 804 with a channel 810similar to that demonstrated by the MEMS die 704, wherein the die 804 ismounted to a substrate 802. A CMOS die 806 (shown in dotted line) isalso mounted to the substrate 802 and is partially nested under the MEMSdie 806. A portion of the CMOS die 806 protrudes through the channel 810in the MEMS die 804. The CMOS die 806 may be connected to the substrate802 by a variety of well known methods, including but not limited to,wire bonding, flip-chip bonding, and through-silicon vias. A sealantmaterial 812, such as silicone, is applied to the sides of the MEMS die804 to seal the channels 810 on both sides of the die and cover the CMOSdie 806. This isolates the volume under the MEMS die 804 from theoutside. FIG. 9 shows an embodiment of a package 901 that includes aCMOS die 906 partially nested under a MEMS die 904 having a channel 910to accommodate the CMOS die 906, i.e., similar to the embodiment of FIG.8. A sealant material 912 is applied to either side of the MEMS die 904over the channel 910 to isolate the back volume 907 from the frontvolume 909. An acoustic port 908 through the cover 903 completes theassembly. In an embodiment, an acoustic port (not shown in the figurebut contemplated based on previously described embodiments) may belocated in the substrate 902 of the package 901. The port may be locatedunderneath or adjacent to the MEMS die 904. These embodiments mayprovide desired sensitivity and signal-to-noise characteristics whilestill providing a reduced overall footprint to the package 901.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Itshould he understood that the illustrated embodiments are exemplaryonly, and should not be taken as limiting the scope of the invention.

1. A package comprising: a substrate; a cover; a MEMS die located on thesubstrate; a CMOS die located underneath the MEMS die having a volume;an acoustic port in the package, wherein the package has a back volumelocated between the MEMS die and the substrate; wherein an effectiveback volume exists which is equal to the back volume minus the volume ofthe CMOS die.
 2. The package of claim 1 wherein the acoustic port is inthe cover.
 3. The package of claim 1 wherein the acoustic port is in thesubstrate.
 4. The package of claim 1 further comprising: a channelcreated within the MEMS die wherein the CMOS die is partially nestedunderneath the MEMS die.
 5. A package comprising: a substrate; a cover;a MEMS die located on the substrate; a CMOS die located underneath theMEMS die having a volume; an acoustic port in the package, wherein thepackage has a front volume located between the MEMS die and thesubstrate; wherein an effective front volume exists which is equal tothe front volume minus the volume of the CMOS die.
 6. The package ofclaim 5 wherein the acoustic port is in the substrate.
 7. The package ofclaim 5 wherein the acoustic port is positioned adjacent to the CMOSdie.
 8. A package comprising: a substrate; a cover; a MEMS die havingsidewalls and a diaphragm connected to the sidewalls; a CMOS diepositioned on the substrate, underneath the MEMS die and surrounded bythe sidewalls of the MEMS die.
 9. The package of claim 8 furthercomprising: an acoustic port within the cover.
 10. The package of claim8 further comprising: an acoustic port within the substrate.
 11. Apackage comprising: a substrate; a cover; a MEMS die having sidewallsand a diaphragm connected to the sidewalls; a CMOS die positioned on thesubstrate, partially underneath the MEMS die and through a channel in asidewall of the MEMS die.
 12. The package of claim 11 furthercomprising: a sealant enclosing a portion of the CMOS die which ispositioned exterior to the MEMS die.
 13. The package of claim 11 furthercomprising: an acoustic port within the substrate.
 14. The package ofclaim 11 further comprising: an acoustic port within the cover.
 15. Apackage comprising: a substrate; a cover; a MEMS die having a diaphragm;a CMOS die wherein at least a portion of the CMOS die is positionedbetween the diaphragm and the substrate.
 16. The package of claim 15wherein the CMOS die is contained within sidewalls of the MEMS die. 17.The package of claim 15 wherein the CMOS die extends through a channelin the MEMS die.
 18. The package of claim 17 further comprising: asealant enclosing a portion of the CMOS die which extends exterior tothe MEMS die.
 19. The package of claim 15 further comprising: anacoustic port within the substrate.
 20. The package of claim 15 furthercomprising: an acoustic port within the cover.